JS Variable Scope

file1.js

var foo = 'hello!';

var util = {
  setBar: function() {
    var bar = 'goodbye!';
  },

  changeFoo: function() {
    foo = 'olah!';
  },

  sayFoo: function() {
    console.log(foo);
  },

  sayBar: function() {
    console.log(bar);
  }
};

util.sayFoo(); // logs 'hello!', because foo was created in a parent scope of util.sayFoo

util.changeFoo();
util.sayFoo(); // logs 'olah!', because changeFoo is modifying the foo created in a parent scope
console.log(foo); // also logs 'olah!'

util.setBar();
util.sayBar(); // errors, because bar was created in a scope outside of util.sayBar
console.log(bar); // also errors, because bar is in a child scope

console.log(fileScoped); // errors, because fileScoped was created in another file

module.exports = 'exported thing';

file2.js

var fileScoped = "you can't see me!"

var thing = require('file1.js');

console.log(thing); // logs 'exported thing', because that was exported from file 1

console.log(foo); // errors, because foo was created in another file
util.sayFoo(); // errors, because util was created in another file